Non-reciprocal devices are used in microwave and optical communications for selectively directing signals from one port to another. With the growth in fiber optic communications, there is an increasing demand for non-reciprocal components that are suitable for use with fiber optic systems. For example, isolators are used for increasing the stability of the frequency and power produced by single mode semiconductor lasers by reducing the power of light feeding back into the laser. As fiber optic systems become more sophisticated, for example with the advent of wavelength division multiplexing (WDM), there is an increased need for advanced components such as optical circulators for use in, for example, multiplexing/demultiplexing and bidirectional transmission.
A variety of circulators can be made. Many circulators have three ports. In these circulators, light incident at the first port is transmitted through the circulator to the second port. This light may then be transmitted to another optical device. Upon returning to the second port, the light is transmitted through the circulator to a third port. Often this third port is close to the first port and, in some cases, the first and third ports include optical fibers held together in contact by a common holder.
Present approaches to circulator design often rely on the use of individual collimating lenses for each fiber. This increases the complexity of aligning the device and necessitates the use of many elements.